Abstract/Project Summary The majority of research invested in combating lung cancer focuses on cancer cell intrinsic drivers, leading to the development of targeted therapies. However, due to genetic plasticity, intratumor heterogeneity, and other evasive mechanisms these regimens always end in patient resistance and relapse. The tumor microenvironment, an emerging hallmark of cancer, provides a myriad of potential therapeutic targets, and yet its role in lung cancer progression remains unknown. We have identified increased numbers of bone marrow derived cells (BMDCs) in the tumor-associated stroma of surgically resected specimens of non small-cell lung cancer (NSCLC). Transcriptome analysis of sorted cell populations identified hundreds of alternatively regulated genes specific to myeloid cells in the tumor bed when compared with normal adjacent lung. The top hit within the microenvironment was Osteopontin (OPN), a secreted phosphoglycoprotein that had previously been associated with lung tumor epithelial cell expression, and whose functional role in vivo remains elusive. Subsequent tumor microarray studies validated the consistent expression of OPN within the intratumoral myeloid cells, but only rarely in the carcinoma cells. Strikingly, the myeloid specificity confers poor prognosis. Further investigation of expression patterns of OPN according to stage revealed a shift in detection from myeloid-confined (early stage) to inclusion of the tumor epithelium (late stage). We believe that addressing the spatiotemporal control of OPN is the key to unraveling its true function in lung cancer progression. Using bone marrow transplantation methods in concert with our stage-reflective lung cancer mouse models, we aim to determine the role of compartment- specific OPN. In addition, protein analysis of OPN in murine tumor-bearing lungs reveals the potential for cell-type specific control of post-transcriptional and post-translational modifications. We will identify these modifications and pursue their functional consequences.